The present invention relates generally to electrical probes and more particularly to an electrical probe for flying leadset logic analyzer probes that accommodates two millimeter pin spacing.
Flying leadsets are logic analyzer probe extensions that allow probing of individual square pin contact of a device under test, such a microprocessor mother board. A leadset consists of a group of electrical probes having contacts that plug onto the square pin contacts mounted on the device under test. Each of the electrical probes of the leadset are electrically coupled to a general-purpose probe of a logic analyzer via a conductive cable. FIG. 1 is a cross-sectional view of an electrical probe 10 for a flying leadset manufactured and sold by Tektronix, Inc., Beaverton, Oreg. The electrical probe 10 has an electrical contact 12 electrically coupled to a resistor 14, which in turn is electrically connected to the center conductor 16 of a conductive cable 18. The electrical contact 12 has a circular central portion 20 with inwardly angled contact fingers 22 extending in one direction from the circular central portion and a flat portion 24 extending from circular central portion in the opposite direction. One lead 26 of the resistor 14 is soldered to the flat potion 24 of the electrical contact and the other resistor lead 28 is soldered to the center conductor 16 of the cable 18. A metal tube 30 is positioned over the contact fingers 22 of the electrical contact 12. One end of the tube 30 extends past the end of the contact fingers 22 and the other end closely fits on the circular central portion 20. A thermoplastic cover 32 is injection molded over the assembled elements with a portion of the metal tube 30 at the distal end of the tube left exposed.
The metal tube serves two purposes: 1) to protect the contact fingers from damage and 2) act as a thermoplastic dam to prevent the injection molded thermoplastic from encapsulating the contact fingers. A drawback to using the metal tube as the thermoplastic dam is that the distal end of the tube is exposed which allows for the possibility of shorts across the square pin contacts or pads of the device under test. A solution to this problem is to substitute a pre-molded thermoplastic cover that is slid down over the assembled elements with the one end of the cover extending down to the end of the metal tube.
Current leadset designs offer users the ability to probe individual pins having centerline-to-centerline pin spacings as close as 0.10 inches. Though this pin spacing is widely used in the electronics industry, closer pin spacings are beginning to become more prevalent. Connectors with two millimeter centerline-to-centerline pin spacings are now being used with compact PCI bus structures. At this spacing, users of the current leadset electrical probes are forced to probe every other pin contact, or bend the pin contacts at allow the electrical probes of the leadset to be grouped side by side.
The present leadset electrical probe design allows the probe to be inserted onto square pin contacts in any orientation. This means that a 0.025 inch square pin contact, which is the prevalent type of square pin contact used in the electronics industry, could deflect the contact fingers of the electrical contact as much as a 0.032 inch diameter round pin. The deflection of the contact fingers is proportional to the stresses in the contact. Excessive deflection of the fingers causes the stress to exceed the elastic limit of the material, thus permanently deforming the fingers and decreasing the pin retention force. decreases the pin retention force of the fingers. Moreover, square pin contacts as small as 0.015 inches are being proposed by the electronic industry. Attempting to make contact on a smaller pin with contact fingers that have been deformed will result in little or no contact force, which can cause intermittent electrical contact between the smaller square pin contacts and the contact fingers.
What is needed is an electrical probe for flying leadsets that allows connection to pin contacts at two millimeter spacing. The electrical probe should also limit the deflection of the contact fingers of the electrical probe to allow reliable electrical connection to various sizes of pin contacts. The electrical probe should also provide protection for the electrical contact without the use of the previously used metal tube.
Accordingly, the present invention is to an electrical probe for a flying leadset of a logic analyzer probe useable with two millimeter spacing contact pins. The electrical probe has coaxially aligned internal elements enclosed in an insulating cover. The electrical probe is configurable as a ground contact probe and a signal probe. The electrical probe has an electrically conductive contact having first and second inwardly angled contact fingers axially aligned with and extending from a support member. The contact fingers have opposing interior surfaces defining a slit there between. The support member has at least a first keying surface formed thereon. The electrically conductive contact further has an axially aligned contact member that extends from the support member in a direction opposite the first and second inwardly angled contact fingers. In the preferred embodiment of the electrical probe, the contact fingers, support member and the contact member are integrally formed.
The ground contact electrical probe has an electrically conductive sleeve axially aligned with and disposed adjacent to the contact member. The sleeve has a bore extending therethough that receives a central conductor of a conductive cable. The central conductor extends through the bore and is secured in the contact member by soldering, crimping or the like of the contact member. The signal electrical probe has a resistive element, such as a resistor, axially aligned with and disposed adjacent to the contact member. The resistive element has electrically conductive contacts extending from opposing ends of the element with one of the electrically conductive contacts secured in the contact member. The electrically conductive sleeve is axially aligned with and disposed adjacent to the resistive element with the other electrically conductive contact of the resistive element extending into the sleeve. The central conductor of the conductive cable also extends into the sleeve. The resistive element contact and the cable central conductor are secured in the sleeve by solder, crimping or the like of the sleeve.
The insulating cover has a contact cover portion and a over-mold portion that are chemically bonded together during overmolding. The contact cover portion has an open end and a closed end with a bore extending part way through the contact cover portion from the open end. The interior of the bore has at least a first interior complementary keying surface to the support member keying surface extending from the open end of the contact cover portion. The open end may be formed with an irregular surface to provide greater surface area for chemical bonding. In particular, the open end of the contact cover portion may be formed with a dove tail recess to both increase surface area for bonding and provide mechanical coupling. The closed end of the contact cover portion has a square aperture formed therein having interior walls intersecting the bore. The keying surface of the support member is positioned relative to the slit between the inwardly angled contact fingers and the complementary keying surface of the bore is positioned relative to one of the interior walls of the square aperture to align the slit parallel with one of the interior walls of the square aperture.
The contact fingers are positioned in the bore of the contact cover portion with the interior complementary keying surface of the bore aligned with and engaging the keying surface of the support member. The open end of the contact cover portion closely fitting over a portion of the support member with the over-mold portion abutting the contact cover portion and encapsulating the other portion of the support member, the resistive element when present, the electrically conductive sleeve and a portion of the conductive cable extending from the sleeve. In the preferred embodiment of the invention, the insulating cover is formed of a thermoplastic material having a maximum side-to-side dimension of up to two millimeters with the square aperture having a maximum side-to-side dimension of up to 0.025 inches.
The objects, advantages and novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawings.